1. Technical Field
Embodiments of the present invention relate to an imaging apparatus, an imaging system, and a method for driving the imaging apparatus.
2. Description of the Related Art
In a field of imaging devices such as CMOS imagers, techniques that enable high resolution and high frame read out have been recently known.
A technique to share circuit elements such as an amplifying transistor among a plurality of photoelectric conversion units for achieving high resolution is known. In this technique, Japanese Patent Application Laid Open No. 2008-219423 describes a technique to achieve a high speed read out.
In the technique described in Japanese Patent Application Laid Open No. 2008-219423, a pixel unit is set to a selected state or a non-selected state by an electric potential of a floating diffusion (referred to as FD hereinbelow) unit, that is, a gate of the amplifying transistor. When a pixel unit in which a plurality of photoelectric conversion units share a single amplifying transistor is set to a selected state from a non-selected state, the electric potential of the FD unit largely changes, requiring a relatively long time for this change of the electric potential to settle. Therefore, when a signal is read out from a pixel of a first row within the pixel unit immediately after the pixel unit is set to the selected state from the non-selected state, the change of electric potential of the FD unit affects the signal that is read out. On the other hand, when signals are read out from a second and subsequent rows after the signal is read out from the first row, the pixel unit maintains the selected state, so the change of electric potential of the FD unit is smaller than that in the first row.
There is an increasing need for high quality images. If the influence of the change of the electric potential of the FD unit differs between the first row and the second and subsequent rows, the obtained image exhibits bright and dark bands. Further, in an image sensing apparatus provided with color filters, when the influence of the change of the FD unit differs between pixels of the same color, correction by a downstream circuitry becomes complex. Accordingly, it is desirable for the difference to be small. The above described change of electric potential may be more recognized when image quality further progresses.